Method of and apparatus for stippling

ABSTRACT

A METHOD OF STIPPLING A DEVELOPMENT BRUSH BY MAKING THE BRUSH CONE-SHAPED AND OSCILLATING IT IN A PLANE COINCIDENT WITH ITS GEOMETRIC AXIS TO CHANGE THE DEGREE OF INTERFERENCE BETWEEN THE BRUSH AND THE SURFACE BEING DEVELOPED.

19.71 p J. M. RANDALL I 3,558,339

. METHOD OF AND APPARATUS FOR STIPPLINGY F iled may 20, 1968 2" Sheets-Sheet 1 i INVENTOR. JOHN M. ANDALL ATTORNEYS 97 1 J. M. RANDIALIL 3,558,339

METHOD OF AND APPARATUS FOR STIPPLING I Filed ma 20,1968 2' sheets-s eet 2 INVENTOR. JOHN M. RANDALL A T TOR/V5 VS United States Patent US. Cl. 117--17.5 4 Claims ABSTRACT OF THE DISCLOSURE A method of stippling a development brush by making the brush cone-shaped and oscillating it in a plane coincident with its geometric axis to change the degree of interference between the brush and the surface being developed.

This invention relates in general to development of a latent electrostatic image, and, in particular, to a method and apparatus for stippling a development brush.

In many copying techniques, such as xerography, a latent image is first formed on a recording surface and then developed with a marking material. In the case of xerography the marking material normally used is a finely divided colored material called toner. In development of latent images with toner a well-known technique is to pass a brush loaded with charged toner particles across the surface bearing the image. By so doing, the charged toner particles, having a charge opposite in polarity to the charged areas of the latent image, are removed from the brush and adhere to the recording member in imagewise configuration. The brush used may be any suitable type which can be loaded with toner particles such as a magnetic brush, fur brush, a brush made with cloth such as velvet having a fibrous surface or other similar material bearing a multiplicity of elongated carrier members on its surface.

Particularly when a fur brush is used to develop a latent image development quality is enhanced by changing the degree of interference between the surface bearing the latent image and the bristles on the fur brush. This technique of development; that is, continuously changing the degree of interference between thebristles and the sur face, is called stippling. It has been found that development quality is a function of the particular stippling technique used.

One common method of stippling when a donor belt is used to carry toner to the latent image is by means of an agitator which causes the belt to vibrate as it passes the area of the latent image. The vibrations cause the toner particles to be shaken off the belt and deposited on the surface bearing the latent image as the agitator moves against the underside of the belt; that is, the surface of the belt opposite the surface carrying the toner particles. In this technique the donor belt is made to vibrate principally in a plane perpendicular to its path of travel there- .by causing the amount of interference between the bristles on the belt and the surface being developed to be altered continuously. A disadvantage of this system is that the belt tends to wear rapidly due to constant flexing through its cross-section as the agitator vibrates it. In addition, the belt constantly changes its degree of tautness around its supporting pulleys as it is agitated making it difficult to keep it traveling in a consistent path.

A second method of stippling a fur belt is disclosed by Walkup in U.S. 3,251,706. As the belt rotates the entire belt assembly oscillates towards and away from the surface being developed. This oscillation causes the bristles on the belt to continuously increase and decrease interference with the surface thereby enhancing image quality. Although the quality of the resulting image is generally Patented Jan. 26, 1971 ICE good when this method ofstippling is employed, development quality is still limited since the belt is stippled only in one plane; that is, the plane perpendicular to the surface being developed.

A third method of stippling is used in conjunction with a development system having a fur brush which is rotated about its geometric axis to place toner on the surface being developed. In this type of system stippling is accomplished by reciprocating the rotating brush in a plane perpendicular to image surface. To assure good image quality the oscillations of the fur brush must be very closely controlled and this requires that elaborate and bulky mechanisms be employed to move the brush. In addition, the only plane in which a cylindrical fur brush can be oscillated to cause uniform stippling across the length of the brush is a plane perpendicular to the geometrical axis of the brush.

Accordingly, it is an object of this invention to provide a method of stippling which overcomes the deficiencies of the prior art devices as described above.

It is a further object to improve the stippling process during development by accurately controlling the interference between a development brush and the surface being developed.

A still further object is to improve apparatus for stippling so that an overall compact development system can be employed.

A still further object is to improve the quality of solid area development by using a cone-shaped development brush.

The present method of stippling uses a cone-shaped development brush which rotates about its geometric axis during development. In order to maintain contact across the surface being developed, the axis of the brush is skewed relative to the plane of the surface bearing the latent image. The stippling action is accomplished by oscillating the brush in a plane which is in alignment with its geometric axis thereby affording improved control of the stippling process and improving development quality.

For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be used in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration showing a typical xerographic device in which the present method of stippling is used.

FIG. 2 is a fragmented, isometric view of a development system having cone-shaped brushes used in the present method of stippling; and

FIG. 3 is a cros-sectional view of a cone-shaped fur brush showing the two extreme positions of the brush during the stippling process.

Referring now to the drawings, FIG. 1 shows a typical xerographic machine in which cone-shaped development brushes can be used. The principal element of the machine is photosensitive member 11. This member consists of drum 12 which is driven about shaft 16 by a motor (not shown). The drum is covered with layer 13 of electrically conductive material which, in turn, is covered on its outer surface with layer 14 of photoconductive insulating material such as vitreous selenium. An electrostatic latent image is formed on member 11 by passing it under sensitizing station 24 and exposing station 17. The sensitizing station consists of any suitable means for placing a uniform charge on layer 14 such as corotron 26; that is, a corona charging device. The exposing station has a light source 23 and lens 18, and transparency 19 feedably disposed between the light source and lens. The transparency is fed from reel 21 through the beam of light generated by source 23 and then rewound on reel 22 after being exposed. The light source, transparency and lens working in combination project on the photosensitive member an optical image whose movement is synchronized with that of the drum. The projected optical image causes selective charge dissipation on areas of layer 14, thus forming an electrostatic image. Other means of forming electrostatic latent images including means for forming images on ordinary insulating surfaces are known in the art and may be used instead of the one shown.

After the sensitizing and exposing steps are completed, the photosensitive member passes through development station 27 which will be described more fully in conjunction with FIGS. 2 and 3. The developing station generally consists of at least one, and preferably two or more, cone-shaped fur brushes 28 and 29 which are loaded with particles of toner 32 which is kept in a loose consistency by auger 31. Housing 35 which surrounds the brushes and auger holds the toner.

Following image development, the image is transferred from photosensitive member 11 to a web of paper or the like 37 between guide rolls 38 and 39 acting to position web 37 against photosensitive member 11 by a second corona discharge device 41. Web 37 is fed from reel 34 before transfer and is rewound on reel 36 after transfer and fusing. A fusing element 42 is positioned to heat the transferred image and thus fix it and permanently bond it to paper web 37. Cleaning station 43 is made up of rotating cylindrical brush 44 which contacts the photosensitive member subsequent to image transfer and removes any residual image material from layer 14, thus readying it for reuse. The above-described process and apparatus are conventional in the art as evidenced in US. Pat. 3,117,891. Any of the many known equivalants of process or apparatus elements may be employed in connection with the present invention.

FIG. 2 is a more detailed illustration of the development apparatus contemplated by this disclosure which is employed to realize the improved method of stippling. Photosensitive member 46 which bears an electrostatic latent image passes adjacent brushes 47 and 48 where the image is developed. The brushes can be of any suitable type by which toner can be transferred to the surface being developed; for instance, magnetic brushes, brushes having pile-like fibers, and natural fur brushes; etc. In the embodiment shown in FIG. 2, natural rabbit fur brushes are used. The fur brushes consist of coneshaped supports '52 and 53 encased by fur pads 49 and 51, respectively. The supports can be non-conductive, rigid members, or, in the alternative, can be made of a conductive material biased with a polarity opposite the polarity existing on the toner particles to improve the ability of the fur pads to hold toner particles.

The fur pads are composed of two distinct, but unified components; a backing material corresponding to the hide of the animal from which the fur pad is made and fibers or bristles which protrude outwardly from the backing material and which carry the toner particles to the surface being developed. The fur pads are secured rigidly to their supports so that as they are rotated all parts of the fur pads pass adjacent to photosensitive member 46. The geometric axis of each of the fur brushes is necessarily skewed relative to the surface which is being developed due to the taper across the length of fur brush. Such skewing of the axes is necessary to assure that the full length of the fur brushes maintain contact with the photosensitive member.

Shafts 57 and 58 are connected to fur brushes 47 and 48, respectively, and are mounted so as to be coincident with the geometric axis of the brushes. These shafts perfonn two functions; rotate the fur brushes to develop the latent image and oscillate the fur brushes to produce a stippling effect during development. Suitable mechanisms 54 and 56 produce the above-mentioned motions on shafts 57 and 58, respectively. The fur brushes are rotated in the same direction relative to each other and both can rotate in either direction relative to photosensitive member 46. Rotation in the above manner has been found to be the best way to develop a latent electrostatic images are exposed to the negatively charged toner partidesirable manner of oscillating the fur brushes is explained in conjunction with FIG. 3.

The fur brushes are loaded with toner material (not shown) which is contained within housing 50. The toner is maintained in a loose consistency due to the turning action of auger 45. As the fur brushes pass through the toner, the bristles rub against the toner particles causing a triboelectric charge to be imparted to the toner particles so acted upon. The use of a fur such as rabbit, as well as the use of a thermoplastic electroscopic toner, causes a positive triboelectric charge to be imparted to the brush bristles. Thus, as the areas of the photosensitive member having positively charged latent electrostatic images are exposed to the negatively charged toner particles, the toner particles will be caused to .adhere to the positively charged surface areas so long as this force of attraction exceeds the force of attraction between the positive brush bristles and the negative toner particles. As a result, the latent images will be visibly defined by the toner particles.

While rotaing about their geometric axes, fur brushes 47 and 48 are stippled by being oscillated along their geometric axes by shafts 57 and 58, respectively. FIG. 3 shows cone-shaped fur brush 64 (cross-section) adjacent photosensitive member 68 which bears the latent electrostatic image being developed. The fur brush consists of cone-shaped support 62 supported by shaft 63 and fur pad 65 fastened securely to the outer periphery of the support. As mentioned above, fur pad 65 consists of a multitude of bristles 67 embedded in backing material 66.

During the stippling process, the fur brush oscillates in a direction parallel to its geometric axis; that is, parallel to shaft 63. The brush position shown by solid lines indicates the location of the brush relative to the photosensitive member when least interference exists between bristles 67 and the photosensitive member. At this position the bristles on the fur brush just barely maintain contact with the surface of photosensitive member 68. On the other hand, the position of the brush shown in dotted lines indicates the location of the brush relative to the photosensitive member when the greatest interference desired exists between bristles 67 and the photosensitive member. In this position, the bristles on the fur brush have contact with thesurface being developed for a greater portion of their length compared to any other position the brush takes during the stippling process.

The two positions shown, the first in solid lines and the second in dotted lines, are representative of the two extreme positions the brush assumes during stippling. It has been found that for achieving optimum quality during development with a rabbit fur brush and conventional toner, the bristles should be stippled from the point where their ends just interfere with the surface being developed to the point where about A" of the bristles interferes with the surface being developed.

Shaft 63, which is securely mounted on fur brush 64, imparts both rotational and oscillating motion to the fur brush. A suitable mechanism (not shown) rotates shaft 63, and thus fur brush 64, in the direction shown by the arrow encircling the shaft. A motor (not shown) can rotate photosensitive member 68 in either direction relative to the direction of the rotation of the fur brush. For instance, the photosensitive member is rotating as shown by continuously between the two extreme positions shown in FIG. 3 causing the degree of interference between the bristles and photosensitive member to change constantly. Because the stippling action occurs by moving the brush in a plane oblique to the surface being developed, better images result. It is believed that such a result occurs because the individual bristles naturally tend to protrude from the backing material in a plane perpendicular to the surface of the backing material and the bristles tend to twist and turn more when stippled obliquely as compared to when stippled perpendicularly as was done previously. Because more surface area of each bristle contacts the surface being developed due to such twisting and turning, more of the toner particles clinging about each bristle are attracted, contact and adhere to the surface bearing the latent image.

Referring back to FIG. 2, although two independent fur brushes are shown, this development system would be operable using merely one brush, or even with a multitude of brushes placed side by side around the photosensitive member. However, it is preferable to use brushes in multiples of two in order to assure uniform toner deposit. When two brushes are used together and especially when their tapers run in opposite fashion to one another, as shown in FIG. 2, images of better quality are produced. Otherwise, since toner deposit is influenced by circumferential area and since the circumferential area of a coneshaped brush inherently varies across its length due to its taper, deposit of toner across the photosensitive surface may be uneven if only one cone-shaped brush is used.

In addition to the apparatus and method outlined above many other modifications and/or additions to this invention will be readily apparent to those skilled in the art upon reading this disclosure, and these are intended to be encompassed within the spirit of the invention.

What is claimed is:

1. A method of applying toner particles to a member having a latent electrostatic charge image thereon comprising the steps of:

uniformly contacting the latent image with bristles supported on a cone-shaped surface and carrying toner particles thereon,

rotating said surface about its geometric axis, and

simultaneously oscillating the surface relative to the member along said geometric axis and to an extent so that the degree of interference between the bristles on the surface and the member is changed constantly to enhance development.

5 2. The method as recited in claim 1 further including the step of simultaneously loading the surface with charged toner particles.

3. A stippling apparatus for applying charged toner particles to a member bearing a latent electrostatic charge 1 image comprising:

a rotatable, cone-shaped surface having bristles thereon positioned in approximately uniform contact with the latent image on the member,

means connected to said surface for rotating the sur- 9 face about its geometric axis, and

means connected to said surface and arranged for oscillating the surface along its geometric axis and in positions wherein said bristles have a low degree of interference with the image and positions wherein the degree of interference between the bristles and the image is greater than said low degree.

4. The apparatus recited in claim 3 in which the surface comprises a fur pad having a backlog material and bristles protruding therefrom, the bristles applying the bulk of the toner particles to the member.

References Cited WILLIAM D. MARTIN, Primary Examiner E. I. CABIC, Assistant Examiner US. Cl. X.R. 

